Formation of thin oxide layers

ABSTRACT

Coating apparatus includes plural chambers having at least restricted communication therebetween to inhibit the transfer of fluid treating material but not of a substrate. A primary treating chamber includes means for supplying a vapor solvent, means for applying a spray solution and means for delivering water vapor. Heating means are provided.

United States Patent Plumat et a1. [451 Aug. 15, 1972 541 FORMATION OFTHIN OXIDE LAYERS 3,488,617 1/1970 Dietrich et a1 ..118/49 x [72]Inventors: Emile Human Gilly; Pierre Bohain 3,491,720 l/1970 Harris ..118/495 Montigniemupsambre Albert 3,181,750 5/1965 Helhwell et a1. ..68/5C vais Gosselms an of Belgium 2,861,897 11/1958 Hendrixsonm. ..118/429 X3,262,420 7/1966 Bossi eta] ..118/57 1 Asslgnefi Glavenben -A- s Belgwm3,197,328 7/1965 Jung et a1. ..1 17/1072 [22] FOREIGN PATENTS ORAPPLICATIONS [2}]. 8156 133,657 7/1949 Australia ..11s/49.1

Related US. Application Data a Primary Examiner-Morris Kaplan [6211138111 5111? f5lS9er461;1O. 639,082, May 17, 1967, Attorney spencer dKaye [30] Foreign Application Priority Data [57] ABSTRACT May 18 1966Luxembourg 51 137 Coating apparatus includes plural chambers having atleast restricted communication therebetween to in- 52] Us Cl l l hibitthe transfer of fluid treating material but not of a 51 1111.ci..IIIIIIII....IIIIIIIIII....IIIIIIfflIIjIlcsc 13/08 Substrate" APrimary "eating Chamber includes means 58 Field of Search ..118/47-501;for Supplying a vapor solvent, means for pp y a 7 10 7 2; 3 5 266/4 3spray solution and means for delivering water vapor. Heating means areprovided. [561 References 5 Claims, 5 Drawing Figures UNITED STATESPATENTS 1,575,926 3/1926 Meurer ..118/303 X 220" EF 7 2 ,1 49 2 0 15 3910a 16 41 40 7 49a 1 4 11a 9b I 9a PATENTEU I972 3.683, 848

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-20b 20a 17 %I g 49 2 19a 4s 1s 39 a 43 L g I 1212 120 15 5 1 40 11b 49a1 11a 9b 9a 14 13! Z INVENTORS Emile P\u.ma Pierre Bolmin Anner: ServaisBY M {@e ATTORNEYS PATENTEDAUB 15 I972 SHEEI 2 0F 3 s oltif T a Nm V. 6Eu f rx w N n 8 0 f er e Maw, Ep y m ATTORNEYS P'ATENTEBAUB 15 I9123.683. 848

sum 3 BF 3 I I i l 31 144 134 3 a I 1 T I 117 11a 5 T T I k k 106INVENTOHS 1 [mile Planner:

Pierre Bel-min Alberc ServaiS BY W 52%:

ATTORNI-YS FORMATION OF THIN OXIDE LAYERS CROSS REFERENCE TO RELATEDAPPLICATION Pat. No. 3,519,467 entitled FORMATION OF THIN OXIDE LAYERBACKGROUND OF THE INVENTION The present invention relates to apparatusfor the surface coating of glass and other materials, and particularlyto apparatus for forming metal oxide coatings of uniform thickness onsuch materials.

It has already been suggested to. form a metal oxide coating, or layer,on materials such as glass by forming the oxide in situ, this involvingfirst applying a solution of a different compound of the metal, i.e., acompound other than the oxide. However, the previouslysuggested-processes of this type have not proven to be completelysatisfactory because they have beenincapable of reliably producingcoatings of uniform thickness and quality. Moreover, in order to carryout these processes, it is necessary to immerse the material in a bathof the metal compound solution, with the result that the processes canonly be employed to simultaneously coat both sides of the glass sheet.

It is therefore a primary object of the present invention to eliminatethese drawbacks and difficulties.

A more specific object of the present invention is to provide apparatuswhich produces improved quality oxide coatings on the surfaces of glassand other objects.

Yet another object of the present invention is to pro vide apparatuswhich produces metal oxide coatings of more uniform thickness. v

Still another object of the present invention is to provide apparatuswhich permits metal oxide coatings to be applied to but one surface of asheet of material.

SUMMARY OF THE INVENTION The present invention is embodied by apparatusfor covering the surface of an object with a metal oxide coating,starting with a compound, other than the oxide, of the metal. Thisapparatus essentially includes at least one first chamber for holdingthe object, first supply means associated with the chamber for fillingit with a vapor of a solvent for the metal compound, and second supplymeans associated with the chamber for applying a solution of the metalcompound to the object after the chamber has been filled with thesolvent vapor. The apparatus further includes at least one furtherchamber for receiving the object after it leaves the first chamber, andheating means associated with the further chamber for maintaining itsinterior at a sufficiently high temperature tooxidize the metalcompound.

The present invention is based on the discovery that a much improveduniformity of the oxide coating is possible if the surface to be coated,when the metal compound solution is applied thereto, has been previouslyprovided with a superficial uniform film of a solvent for the metalcompound. This solvent may be the solvent, or one of the solvents, usedfor forming the solution of the metal compound, or some other solventcompatible with the solvents used in such solution. It is important toavoid any premature conversion, i.e., oxidation, of the dissolved metalcompound because this conversion must commence only when the solution ispresent in the form of a barely perceptible layer on the surface to becoated. Consequently water vapor must be excluded from the atmosphere towhich the solventmoistened surface is exposed and in which the metalcompound solution is applied.

The invention can be applied for coating glass, ceramic, polished metal,plastics and other surfaces. However, the invention is employedprimarily for coating glass, particularly glass in sheet form, and it isfor that reason that the present invention will be described withspecific reference to such material.

The reasons for the improved results obtainable as a result of thepreparatory moistening of the glass surface with solvent, preferably anorganic solvent, are not known with certainty. It is remarkable thatthis preparatory slight wetting, or moistening, is of such effect that avery uniform metal oxide coating can be formed even if the metalcompound solution is poured or sprayed onto the moistened surface. Byway of comparison, in order to obtain uniformity in the prior artprocesses, it was necessary to apply the metal compound solution bydipping the glass into the solution and even then the best resultsobtainable did not equal those which can be realized by the presentinvention. It is to be understood, however, that the technique ofapplying the metal compound solution by immersion of the surface to becoated in a mass of the solution, e.g., by dipping the sheet glass orother article so as to coat more than one surface, is not excluded fromthe scope of the invention, although this is not the preferredprocedure.

The preparatory treatment of the surface is described as a lightwetting" or moistening to indicate it is carried out in such a way as toleave no excess solvent liquid on the surface when the metal compoundsolution is applied, the film of solvent being only just perceptible ornot perceptible at all under ordinary observation. The manner in whichthis slightly moist condition of the surface is obtained is not criticalbut the preferred method is to expose the surface to a vapor of theselected solvent (which may be a single compound or a mixture ofcompounds) by disposing it in an enclosure filled with such vapor. Theconditions of this treatment may be, and preferably are, such that thevapor concentration is near to the saturation point. However,condensation of solvent in the form of apparent droplets on the surfacemust be prevented. Another method comprises thoroughly wetting thesurface with the solvent, by a dipping or rinsing treatment orotherwise, and then drying the surface to a point at which an invisibleor just perceptible uniform solvent film remains.- The solvent maycontain a wetting agent or surfactant. The precise point at which dryingmust be terminated when using this alternative method is not easy todetemiined however, so that the vapor contact method is much preferred.Whatever method be adopted, the surface to be treated should of coursebe thoroughly clean. I

The metal compound solution is preferably applied by spraying or pouringthe solution onto the surface while it is maintained in the solventvapor atmosphere used for producing the preparatory moistening.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional,elevational view of one embodiment of apparatus according to theinvention.

FIG. 2 is a side elevational view taken along the line 2-2 in FIG. 1.

FIG. 3 is a cross-sectional, elevational view of another embodiment ofapparatus according to the invention.

FIG. 4 is a cross-sectional, elevational view of a third embodiment ofapparatus according to the invention.

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Apparatus according to thepresent invention is arranged to conduct articles to be coated from achamber or chambers in which the solvent vapor atmosphere can beestablished and the metal compound solution applied, to a followingchamber or chambers in which conversion of the applied metal compound orcompounds takes place in situ to form a metal oxide coating on thearticles. Apparatus according to the invention includes a chamber orchambers equipped with means for charging it or them with solvent vaporand with means for discharging metal compound solution onto an articlebeing held in a solvent vapor atmosphere in the, or a, chamber, and afurther chamber or chambers into which articles can be conveyed from thefirst chamber or chambers and which is equipped with heating means formaintaining the interior of the further chamber or chambers at anelevated temperature. The

apparatus preferably comprises an article transportation device fortransporting articles from one chamber to the next.

In the apparatus shown in FIGS. 1 and 2 there are provided threesuperimposed chambers l, 2, 3.

The bottom chamber 1 is defined by side walls 4 and 5, front and rearwalls 6 and 7 and a base 8. Pipes 9a, 9b, 9c, 9d, 10a, 10b, 10c, and 10dhaving valves 11a, 11b, 11c, 11d, 12a, 12b, 12c, and 12d respectively,extend through the lower and upper portions of the side walls 4 and 5and the longitudinal walls 6 and 7, respectively. An evacuation conduit13 having a valve 14 extends through the base 8. Between the chamber 1and the chamber 2 there are four shutters, or partitions, 15 which canbe retracted into respective housings 16.

The front, rear and side walls of chamber 1 are up wardly prolongated tofonn the front, rear and side walls of chambers 2 and 3. The side wallsof chamber 2 are indicated at 17 and 18. The chamber 2 has lower andupper pipes corresponding to the pipes 9a-9d and l0a-10 of chamber 1.FIG. 1 shows two of the lower pipes 190 and 19b and two of the upperpipes 20a and 20b of chamber 2 and their respective valves 21a, 21b, 22aand 22b respectively. Between the chamber 2 and the top chamber 3 thereare four shutters, or partitions, 23 shown retracted into theirrespective housings 24.

The side walls of chamber 3 are indicated at 25 and 26. This chamberlikewise has four lower and four upper pipes fitted with valves. FIG. 1shows two of the lower pipes 27a and 27b and their respective valves 29aand 29b, and two of the upper pipes 280 and 28b and their respectivevalves 30a and 30b. At the top of chamber 3 there are four shutters, orpartitions, 31

' shown retracted into their respective housings 32.

The side walls of the chambers are prolongated upwardly to providesupports 33 and 34 for pulley wheels 35 and 36. Cables 37 and 38 runover these wheels and extend downwardly to a horizontal bar 39. Theother ends of the cables 37 and 38 are wound on a motor driven drum (notshown). A series of tongs 40 are fitted onto the bar 39 so that a sheetof glass 41 can be suspended from the bar as shown, and this sheet canbe readily lowered into and raised through the chambers l, 2 and 3.

At the upper portion of the chamber 1 there is a spray pipe 42 the endsof which are connected to pipes 43 and 44 which have valves 45 and 46,respectively, and which are connected to reservoirs 47 and 48,respectively, holding quantities of a liquid 49. The reservoirs 47 and48 are supported by brackets 50 and 51 attached to the side walls 17 and18 of chamber 2.

The apparatus shown in FIGS. 1 and 2 functions as follows:

After a sheet of glass, such as sheet 41, has been lowered into thechamber 1, the shutters 15 are closed so as to substantially isolatethis chamber from chamber 2. Solvent vapor, at ordinary temperature,e.g., ethyl alcohol vapor, is then admitted into chamber 1 through pipes9a-9d and Illa-10d so that the chamber becomes filled with the vapor upto a concentration approaching the saturation point. Subsequently, andwhile the chamber 1 remains filled with the alcohol vapor, the valves 45and 46 are opened so that the liquid 49 is released from the reservoirs47 and 48 and discharges from pipe 42 in the form of sprays 49a over oneface, face 52, of the glass sheet. In an actual example, wherein thevapor supplied to the chamber 1 was an ethyl alcohol vapor as abovereferred to, the solution sprayed onto the sheet from pipe 42 may be asolution formed by dissolving titanium chloride in ethyl alcohol, thesolution having a viscosity of about 2 centipoises and containing, perliter of solution, sufiicient titanium to form 8 grams of TiO Over aperiod of 1 minute, a quantity of the solution equivalentto 1 liter persquare meter of the sheet surface 52 is sprayed onto this surface. Theface 52 thereby becomes covered by a layer 53 of the solution, as shownin FIG. 2. The surplus liquid 49a which runs off the surface 52 of theglass sheet collects in the lower portion of the chamber 1 and issubsequently removed via the conduit 13 by opening valve 14, afterhaving taken the precaution of closing the valves Ila-11d and l2a-12d toprevent any loss of vapor from the vapor supply source. As soon as thesurplus solution has been evacuated, the valve 14 is closed. Then thepipes 10a, 10b, 10c and 10d are connected to another reservoir (notshown) containing air having a relative humidity of about 30 percent,and the evacuation conduit 13 is connected to another reservoir (notshown) which is itself connected to a device for maintaining theinterior of this other reservoir at sub-atmospheric pressure. The valves12a, 12b, 12c, 12d and 14 are then opened to allow the alcohol vapors inchamber 1 to be sucked into the reduced pressure reservoir. At the sametime the chamber becomes charged with the air at 30 percent relativehumidity and the titanium compound in the coating solution hydrolyzes.

After the evacuation of the alcohol vapors, the shuttexs 15 areretracted into their housings 16 and the coated glass sheet is raisedinto the chamber 2. Once the sheet is located in the chamber 2 and theshutters l5 and 23 are closed, the valves of the lower pipes of chamber2 are opened and air heated to 70 C enters the chamber through thesepipes from a source (not shown). In this way the organic solvent stillremaining in the layer 53 is rapidly removed. In one actual processusing the illustrated apparatus, the coated sheet was left in chamber 2for 6 minutes at a temperature of 70 C. After the drying in chamber 2has been completed, the shutters 23 are retracted into their housings24, and the sheet of glass is quickly raised into the chamber 3 foroxidizing the coating 53. In order to avoid subjecting the glass sheetto a thermal shock on transfer to the chamber 3, this chamber ispreheated to a temperature of about 70 C by the admission of air havinga temperature of 70 C into the chamber through pipes 27a and 27b whilethe shutters 23 and 31 are closed. The shutters 31 remain closed whenthe shutters 23 are opened to allow the glass sheet to be raised intothe chamber 3. Once the sheet is in chamber 3, the shutters 23 areclosed again. The output from the heaters (not shown), which may be ofany well-known type, used for heating the air admitted to chamber 3 isthen stepped up and the temperature in chamber 3 is progressively raisedto about 450 C. This temperature is maintained for about minutes so thatthe layer is adequately oxidized, the titanium hydroxide becomingconverted to titanium oxide. At the end of the oxidation stage thetemperature of the air supplied to the interior of the chamber 3 isgradually lowered so that the sheet is gradually cooled in preparationfor being withdrawn into the ambient air. By the above-describedprocedure a titanium dioxide layer of the order of 60 rnillimicrons inthickness can be formed.

The apparatus shown in FIGS. 1 and 2 is suitable for use in formingmetal oxide coatings on small quantities of glass sheets.

It should be noted at this point that the thickness of the resultingmetal oxide layer depends to a large extent on the concentration of thesolution so that the possibility of controlling the coating thickness bycontrolling the concentration of the solution applied to the surface isof potential importance particularly in the coating of glass to formoptical layers of various thicknesses.

The density of the solvent vapor atmosphere employed for the preparatorytreatment of the surface, and the length of time during which thesurface is exposed to this atmosphere, are also factors which influencethe thickness of the metal oxide layer eventually formed. These factorshave independent influences so that, for example, the coating thicknesscan be altered by lengthening or shortening the time during which thesurface is in a solvent vapor atmosphere of given density. I

The preferred methods of applying the metal compound solutionare, asalready mentioned, by spraying or pouring, the most preferred methodbeing spraying, and when employing these methods the solution can easilybe applied to one side only of the article to be coated, e.g., one sideof a glass sheet. During application of the solution, the surface mayhave any desired orientation. In general, when coating material in sheetform, the most convenient orientation of the sheet in a mass processingplant involving automated transportation of the sheets through theprocessing unit is either vertical or horizontal.

The conditions under which the conversion of the dissolved metalcompound or compounds takes place to form the metal oxide coating insitu depend on the nature of the dissolved metal compounds. Whenemploying the invention for forming a titanium oxide coating theconversion may be achieved, as described in detail above, by apreliminary hydrolysis followed by heating until all of the solvent hasevaporated.

The invention is primarily intended to be applied for forming coatingscomposed of a single metal oxide but coatings composed of oxides of twoor more metals can be formed by using a metal compound solutioncontaining different metal compounds convertible to different oxides.

FIG. 3 shows an apparatus according to the present invention which ismore suitable for coating large quantities of sheets on a massproduction basis. In this apparatus there are three side-by-sidechambers 54, 55 and 56 through which sheets to be coated can be conveyedin the direction indicated by the arrow 57. The chambers are bounded bytwo parallel longitudinal walls and by transverse walls 58, 59, 60 and61. These transverse walls include displaceable panels, or partitions,62, 63, 64 and 65, respectively, which can be raised into housings 66,67, 68 and 69, respectively. The three chambers 54, 55 and 56 are closedat the top by top walls 70, 71 and 72, respectively. Two pipes extendinto each chamber through its top wall. Thus, chamber 54 has two pipes73 and. 74 fitted with valves 75 and 76, respectively, chamber 55 hastwo pipes 77 and 78 fitted with valves 79 and 80, respectively, andchamber 56 has two pipes 81 and 82 with valves 83 and 84, respectively.

At the bottom of the chamber 54 there is a ceramic base 85. At thebottom of chamber 55 there is a metal sump 86 with an evacuation conduit87 having a valve 88. At the bottom of chamber 56 there is a ceramicbase 89.

A rail 90 extends through the three chambers 54, S5 and 56 and serves asa track for rollers 91 carrying tongs 92 for the attachment of glasssheets 93, 94 and 95.

In the upper portion of chamber 55 there is a spray pipe 96 which isconnected, via a pipe 97 having a valve 98, to a reservoir 99 supplyinga liquid 100. The reservoir 99 is supported by brackets 1101 and 102attached to the housings 67 and 68.

The installation illustrated in FIG. 3 operates as follows:

Once a sheet of glass, such as sheet 93, has moved into chamber 54, thepanel 62 is lowered. The panel 63, which will normally be raised whenpanel 62 is raised to permit a glass sheet already treated in chamber 54to pass from that chamber into chamber 55, is likewise lowered. Solventvapors at normal room temperature are then admitted into chamber 54through pipes 73 and 74. The vapor concentration is progressivelyincreased up to a point close to the saturation point.

Subsequently, the panel 63 is raised and the sheet 93 is moved intochamber 55 to the position shown for sheet 94 in the drawing and at thesame time sheet 94 moves on into chamber 56, panel 64 being raised justprior to this movement. As soon as sheet 93 moves into position inchamber 55, the panels 63 and 64 are lowered. Chamber 55 is filled withsolvent vapors at normal room temperature, the vapors being admittedthrough pipes 77 and 78, so that the nature of the atmosphere in contactwith a sheet does not change when the sheet moves from chamber 54 tochamber 55.

While sheet 93 is in chamber 55 one face of the sheet is sprayed withthe solution 100, which is a solution of a metal compound dissolved in aquantity of the same solvent as that which constitutes the vaporatmosphere. This solution is released from reservoir 99 by opening valve98 and issues from pipe 96 in the form of sprays 100a. The sprayingcontinues for about one minute during which time a quantity of thesolution 100 corresponding to about 1 liter per square meter of thesurface to be coated flows down this surface so as to cover it with aliquid layer similar to the layer 53 shown in FIG. 2. The surplussolution collects in the sump 86 and is eventually discharged throughthe conduit 87 by opening the valve 88, after taking the precaution ofclosing the valves 79 and 80 to shut off the supply of solvent vapors.

Valve 88 is then closed, after which solvent vapors remaining in thechamber 55 are evacuated in the following manner. First, the pipes 77and 78 are placed in communication with another reservoir (not shown)containing air having a relative humidity of about 30 percent and theevacuation conduit 87 is placed in communication with a reservoir (notshown) the interior of which is maintained at sub-atmospheric pressure.The valves 79, 80 and 88 are then opened so that the solvent vapors inthe chamber 55 become drawn off and replaced by air having a relativehumidity of about 30 percent.

After this treatment of the sheet in chamber 55 with humid air, thepanels 62, 63, 64 and 65 are raised and sheet 93 moves into chamber 56.At the same time, the sheet previously in that chamber moves out of theapparatus and the place occupied by sheet 93 in chamber 55 becomesoccupied by a following sheet from chamber 54. Once the sheets havetaken up their new positions, the panels 62, 63, 64 and 65 are closedagain. The valves 83 and 84 are then opened to admit air heated to 90 Cinto the chamber 56 to cause the organic solvent still remaining in thelayer covering the coated surface of sheet 93 to be rapidly eliminated.

The oxidizing of the coating layers on the sheets leaving the apparatusof FIG. 3 may be achieved by moving the sheets through a furtherenclosure between infrared lamps, for example.

In an actual process using apparatus as shown in FIG. 3, the vaporcontact treatment was carried out using butyl alcohol and the solutionapplied through spray pipe 96 was a solution of titanium chloride inbutyl alcohol containing, per liter of solution, an amount of titaniumsufficient to form 20 grams of TiO:. Any type of butyl alcohol can beused, such as CI-L, CH CH CH OI-I, for instance.

The drying in chamber 56 took place at a temperature of 90 C and lastedminutes. Firing of the coating layer was achieved by heating the coatedsheet to a temperature of 400 C for minutes. A thin layer of titaniumoxide was obtained which had a uniform thickness of the order of 150millimicrons.

The apparatus shown in FIGS. 4 and 5 includes a conveyor 103 (FIG. 5)composed of vertical side supports 104, horizontal members 105, andsheet transporting rollers 106 mounted between members for conveyinghorizontally oriented sheets to be coated through three chambers 107,108 and 109, in the direction of arrow 110 (FIG. 4). The three chambers107, 108 and 109 have lower portions in the form of tanks 111, 112 and113, respectively, and upper cover portions 114, 115 and 116,respectively. The tanks 111-113 are carried by the vertical sidesupports 104 (connection not shown), and the cover portions 114-116 aresupported by plates 117 and 118 each welded to a respective horizontalmember 105. The successive chambers 107, 108 and 109 are connected topairs of pipes 119-120, 121-122 and 123-124, respectively. These pipesare fitted with valves 125-126, 127-128, 129-130, respectively.

By virtue of the fact that the cover portions are spaced slightly abovethe lower tank portions of the chambers, each chamber has a respectiveinlet slot 131, 132, or 133 and a respective outlet slot 134, 135, or136, each slot being just high enough to permit the passage of the glasssheets to be coated. The middle chamber 108 is provided with anevacuation conduit 137 having a valve 138, and a spray pipe 139 disposedhorizontally within the chamber and supplied, via a pipe 140 having avalve 141, from a reservoir 142. When valve 141 is opened to releasemetal compound solution 143 from the reservoir 142, the liquid issprayed onto the top surfaces of successive glass sheets 146, 145 and144 as they are conveyed through the chamber, the spraying occurringcontinuously, as each sheet passes under spray 143a, to form a metalcompound solution layer 147 on each sheet.

The apparatus shown in FIGS. 4 and 5, functions in a manner similar tothat of the apparatus shown in FIG.

3, except that the sheets to be coated are transported in a horizontalposition through the chambers-for the successive processing treatmentsand the chambers are 9 provided with horizontal slots'for the passage ofthe sheets. These slots permit only restricted communication between thethree chambers and between chambers 107 and 109 and the atmosphere, andthe provision of displaceable partitions or panels is not necessa- Asstated before, it is possible to add to the solvent a wetting agent orsurfactant, for instance alkyl benzene sulfonate of sodium, sodiumtripolyphosphat'e, The concentration to be used is about 1 percent.

Other compounds to which the process according to the invention appliesto form a metal oxide layer are titanium-, tin-, zirconium-, chromium-,zinc-butylate,- ethylate,- propylene glycolate, or phenylglucidate. Whenusing the latter, the alcohol is first dissolved incarbon-tetrachloride.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range equivalents of the appended claims.

CLAIMS 1. Apparatus for covering the surface of an object with a metaloxide coating, starting with a compound, other than the oxide, of themetal, comprising, in combination:

f. heating means associated with said furtherchamber for maintaining itsinterior at a sufficiently high temperature to oxidize the metalcompound; I

g. evaporation means associated with one of said chambers forevaporating the solvent remaining on an object after the solution of themetal compound has been applied thereto and before the metal compoundhas been oxidized; and

h. means for preventing substantial communication between each saidchamber and the region exterior thereto at least while an object isbeing treated therein while permitting an object to pass into and out ofsaid chambers without contacting said preventing means.

2. An arrangement as defined in claim 1 further comprising objecttransportation means arranged for transporting objects from one of saidchambers to the next.

3. An arrangement as defined in claim 1 further comprising meansassociated with said second supply means for controlling the amount ofmetal compound solution supplied to said second supply means.

4. An arrangement as defined in claim 1 further comprising meansassociated with said first supply means for controlling theconcentration of solvent vapor in said first chamber.

5. Apparatus for covering the surface of an object with an optical metaloxide coating, starting with a compound. other than the oxide, of themetal, comprising, in combination:

a. at least one first chamber for holding the object;

b. first supply means communicating with said first chamber for fillingit with a vapor of a solvent for the metal compound;

c. second supply means, including spray means, communicating with theinterior of said first chamber for applying a layer of a solution of themetal compound to the, object at the earliest during the contacting ofthe object with the vapor;

d. third supply means communicating with the interior of said firstchamber forfilling it with water vapor, after the metal compound hasbeen applied, to achieve a preliminary hydrolysis of the metal compoundlayer on the object;

e. at least one second chamber disposed for receiving a coated objectafter it leaves said first chamber;

f. heating means associated with said second chamber for heating acoated object therein to a temperature suflicient to convert suchcoating into a dry metal oxide;

g. evaporation means associated with one of said chambers forevaporating the solvent remaining on an object after the solution ofthemetal compound has been applied thereto and before the metal (1 h be 'd'd; d g. rl a s socl ted ailll ezl h chamber for substantially isolatingit from its surroundings at least while an object is being treatedtherein while permitting an object to pass into and out of said chamberswithout contacting said isolating means.

g g UNITED STATES PATENT OFFICE 1 i a CERTIFICATE OF fiORRECTION Patentno. 3,683,848 Dated Axgust 15th, 1972 Invent0 )Emile Plumat, PierreBohain and Albert Servais It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading of the patent, line 5 change "Glavenben" to -Glaverbel-.Column 2, line 61, change "determined" to -determine-. Column 3 line 54change "10a 10" to l0a l0d. Column 10 line 32 before "means" change "g.to -h..

Signed and sealed this 17th day of April 1973 (SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM P (10459) USCOMM-DC scam-m9 .5. GOVERNMENT FRINTINGOFFCE: I969 O'3 33 H

2. An arrangement as defined in claim 1 further comprising objecttransportation means arranged for transporting objects from one of saidchambers to the next.
 3. An arrangement as defined in claim 1 furthercomprising means associated with said second supply means forcontrolling the amount of metal compound solution supplied to saidsecond supply means.
 4. An arrangement as defined in claim 1 furthercomprising means associated with said first supply means for controllingthe concentration of solvent vapor in said first chamber.
 5. Apparatusfor covering the surface of an object with an optical metal oxidecoating, starting with a compound, other than the oxide, of the metal,comprising, in combination: a. at least one first chamber for holdingthe object; b. first supply means communicating with said first chamberfor filling it with a vapor of a solvent for the metal compound; c.second supply means, including spray means, communicating with theinterior of said first chamber for applying a layer of a solution of themetal compound to the object at the earliest during the contacting ofthe object with the vapor; d. third supply means communicating with theinterior of said first chamber for filling it with water vapor, afterthe metal compound has been applied, to achieve a preliminary hydrolysisof the metal compound layer on the object; e. at least one secondchamber disposed for receiving a coated object after it leaves saidfirst chamber; f. heating means associated with said second chamber forheating a coated object therein to a temperature sufficient to convertsuch coating into a dry metal oxide; g. evaporation means associatedwith one of said chambers for evaporating the solvent remaining on anobject after the solution of the metal compound has been applied theretoand before the metal compound has been oxidized; and g. means associatedwith each said chamber for substantially isolating it from itssurroundings at least while an object is being treated therein whilepermitting an object to pass into and out of said chambers withoutcontacting said isolating means.